A liquid processing process is one of various processes of manufacturing a semiconductor device. In the liquid processing process, a substrate such as, e.g., a semiconductor wafer is processed by rotating the substrate around a vertical axis line and supplying a processing liquid to the rotating substrate. When performing the liquid processing process, for example, if the substrate is laid on the substrate holding member without being properly held by the substrate holding member, there is a concern that the substrate may be damaged by falling off from the substrate holding member due to the rotation. Thus, it is necessary to confirm whether the substrate is properly held before starting the processing.
Japanese Patent Laid-Open Publication No. H8-316290 discloses a rotary substrate processing apparatus including a substrate holding state determination means configured to optically confirm a substrate holding state of a substrate holding member. The substrate holding state determination means is provided with plural sets of light projectors and light receivers and a light projector and a light receiver of each set are disposed outside of circumferential edge portion of the substrate to be opposite to each other in the diametric direction of the substrate. The substrate processing apparatus of Japanese Patent Laid-Open Publication No. H8-316290 is provided with an elevatable cup configured to receive a processing liquid supplied to a rotating substrate and scattered to the outside by centrifugal force when the processing is performed. The projector and the light receiver of each set are disposed to be positioned at the outside of the cup which is at a raised position. The holding state of the substrate is determined when the cup is at a lowered position. When it is determined that the retaining state of the substrate is proper, the cup moves to the raised position surrounding the substrate, the processing liquid is supplied to the rotating substrate, and a predetermined liquid processing is performed in this state.
The substrate holding state determination means of Japanese Patent Laid-Open Publication No. H8-316290 may confirm the holding state only when the cup is located at a height lower than the substrate so that the surrounding space of the circumferential edge of the substrate is opened. That is, the substrate holding state determination means of Japanese Patent Laid-Open Publication No. H8-316290 may not be applicable to a substrate processing apparatus which is configured such that a substrate holding operation of the substrate holding member is performed within the cup. Although above limitation may be resolved by disposing a light projector and a light receiver within the cup, it is not desirable to dispose the light projector and the light receiver within the cup considering a wet environment or a corrosive environment within the cup.